[PATCH v2 3/4] block: loop: introduce 'use_aio' sysfs file

[Ming Lei <ming.lei@canonical.com>]

So that users can control if kernel aio is used to submit I/O.

Signed-off-by: Ming Lei <ming.lei@canonical.com>
---
 drivers/block/loop.c |   33 +++++++++++++++++++++++++++++++++
 drivers/block/loop.h |    1 +
 2 files changed, 34 insertions(+)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index d1f168b..47af456 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -659,6 +659,38 @@ static ssize_t loop_attr_partscan_show(struct loop_device *lo, char *buf)
 	return sprintf(buf, "%s\n", partscan ? "1" : "0");
 }
 
+static ssize_t loop_attr_do_show_use_aio(struct device *dev,
+				struct device_attribute *attr, char *buf)
+{
+	struct gendisk *disk = dev_to_disk(dev);
+	struct loop_device *lo = disk->private_data;
+
+	return sprintf(buf, "%s\n", lo->use_aio ? "1" : "0");
+}
+
+ssize_t loop_attr_do_store_use_aio(struct device *dev,
+		struct device_attribute *attr, const char *buf,
+		size_t count)
+{
+	struct gendisk *disk = dev_to_disk(dev);
+	struct loop_device *lo = disk->private_data;
+	int err;
+	unsigned long v;
+
+	err = kstrtoul(buf, 10, &v);
+	if (err < 0)
+		return err;
+	if (v)
+		lo->use_aio = true;
+	else
+		lo->use_aio = false;
+	return count;
+}
+
+static struct device_attribute loop_attr_use_aio =
+	__ATTR(use_aio, S_IRUGO | S_IWUSR, loop_attr_do_show_use_aio,
+			loop_attr_do_store_use_aio);
+
 LOOP_ATTR_RO(backing_file);
 LOOP_ATTR_RO(offset);
 LOOP_ATTR_RO(sizelimit);
@@ -671,6 +703,7 @@ static struct attribute *loop_attrs[] = {
 	&loop_attr_sizelimit.attr,
 	&loop_attr_autoclear.attr,
 	&loop_attr_partscan.attr,
+	&loop_attr_use_aio.attr,
 	NULL,
 };
 
diff --git a/drivers/block/loop.h b/drivers/block/loop.h
index 301c27f..15049e9 100644
--- a/drivers/block/loop.h
+++ b/drivers/block/loop.h
@@ -57,6 +57,7 @@ struct loop_device {
 	struct list_head	write_cmd_head;
 	struct work_struct	write_work;
 	bool			write_started;
+	bool			use_aio;
 	int			lo_state;
 	struct mutex		lo_ctl_mutex;
 
-- 
1.7.9.5